(1) Field of the Invention
The present invention relates to a method of drying honeycomb structural bodies in which a dielectric drying is performed by moving the honeycomb structural bodies in a dielectric drying apparatus under a condition such that vapor is flowed in the dielectric drying apparatus.
(2) Prior Art Statement
Generally, when the honeycomb structural body formed from a batch containing water component is dried, a dielectric drying utilizing the dielectric drying apparatus is performed. Specifically, a dielectric drying is performed by moving the honeycomb structural body in the dielectric drying apparatus as follows. That is, the honeycomb structural body is set on a carrier in such a manner that one end portion of the honeycomb structural body is contacted to a surface of the carrier, and the carrier is moved under a condition such that vapor is flowed in the dielectric drying apparatus so as to prevent a cutout defect of an outer wall.
The method of drying the honeycomb structural bodies utilizing a known dielectric drying mentioned above is sufficient for drying the known honeycomb structural body with no defects in which a thickness of a rib is relatively thicker or in which a size (outer diameter, length) is small. However, in the case that a thin wall honeycomb structural body having a rib thickness of for example 2 mill or less, that is recently required, is dried, a so-called rib twist defect, in which the rib is not generated straight at the end portion of the honeycomb structural body as shown in FIGS. 2 and 3, occurs frequently. If such a rib twist defect is generated, a strength of the honeycomb structural body is decreased, and it is not possible to obtain normal honeycomb structural bodies. Therefore, it is desired to develop a technique for preventing the rib twist defect.
An object of the present invention is to eliminate the drawbacks mentioned above and to provide a method of drying honeycomb structural bodies in which defects such as rib twist and so on are not generated during a drying operation even if a thin wall honeycomb structural body is dried.
According to the invention, a method of drying honeycomb structural bodies in which a dielectric drying is performed by moving the honeycomb structural bodies in a dielectric drying apparatus under a condition such that vapor is flowed in the dielectric drying apparatus, comprises the steps of: covering a surrounding area of the honeycomb structural body by a sheet with a constant space; and performing the dielectric drying under such a condition.
In the present invention, since the surrounding area of the honeycomb structural body is covered by the sheet with a constant space during the dielectric drying operation, it is possible to increase humidity around an outer wall of the honeycomb structural body, and a wind flowing in the dielectric drying apparatus is not directly contacted to the outer wall. Therefore, a drying of the outer wall can be slow, and drying speeds at the outer wall and at inner portion of the honeycomb structural body are substantially same. In this manner, a drying balance of the honeycomb structural body can be achieved, and thus it is possible to prevent the defect generation such as rib twist and so on during the drying operation.
As a preferred embodiment of the present invention, there are following features such that: a Teflon(copyright) fluorocarbon resin sheet is used as the sheet; a dielectric drying is performed under a condition such that additional electrodes are set directly to both end portions of the honeycomb structural body on the carrier of the dielectric drying apparatus; and the space between the honeycomb structural body and the sheet is set to 20 -30 mm. In all the preferred embodiments mentioned above, it is possible to prevent the rib twist defect more effectively, and thus they are the preferred embodiments.